James Duncan Davidson - noted photographer and software developer - has played with image delivery for Retina quite a bit. He details much of it on his blog: http://duncandavidson.com/blog/2012/08/retina_ready

Essentially he currently uses Picturefill (https://github.com/scottjehl/picturefill). From Davidsons' blog: "It’s a compact bit of JavaScript which supports a syntax that mimics the Picture Element Proposal. In a nutshell, it uses CSS media queries to sort out the most appropriate image to use out of a set."

Looks promising.